1. Field of the Invention
The invention relates generally to a method and apparatus for side-fill manufacturing of lenses.
2. Description of Related Art
In manufacturing lenses and particularly those lenses made with thermosetting resins in mold assemblies, it is essential to distribute the resin for good replication of mold surfaces. However, when an embedded layer, such as a polarizing film or wafer, is positioned within the mold assembly it hinders resin distribution. This hindrance results in poor resin coverage on the front surface of the embedded layer, which leads to damage in subsequent processing. Additionally, non-uniform resin distribution results in displacement or distortion of the embedded layer, ruining the product lens. Furthermore, uneven resin distribution causes the trapping of air within the mold assembly, which also ruins the product lens. There have been attempts to avoid the problems associated with resin distribution around embedded layers. It has been reported that embedded layers have tabs or cut-outs along the layer""s edge to allow flow of a thermosetting resin from one side of the layer to the other. [Roscrow, et al., U.S. Pat. No. 4,522,768]. It has also been reported to use shims under a polarizer or use tab cuts in a polarizer to allow resin flow around the embedded layer. [Laliberte, U.S. Pat. No. 4,090,830]. A lens manufacturing process has been reported which allows sequential resin introduction into a mold, the placement of an embedded layer, followed by a second resin introduction into the mold. [Blum, U.S. Pat. No. 4,873,029]. The sequential layered construction disclosed is time consuming and therefore more susceptible to error and variation. Thus, the features disclosed are insufficient to achieve high yields because of non-uniform distribution and uncertainty of repeatability of positioning.
Another problem associated with the use of thermosetting materials for casting lenses is the control of the precise distribution of resin within the mold assembly. For example, an equal thickness of thermoset resin may be desired in making finished plano lenses. However, a controlled but unequal distribution of resin may be desired in making a semi-finished lens blank, which may be further surfaced to ophthalmic prescriptions.
Yet another problem associated with manufacturing lenses in mold assemblies is that gases are often entrapped within the mold assembly. A gasket having two identical fill/vent holes has been reported [Orlosky, U.S. Pat. No. 4,693,446]. However, Orlosky required the fill vent holes to be at the top of the gasket, requiring the exhaust air, as well as the reactive monomer mixture, to execute a right angle turn to a narrowed channel. Orlosky also required the fill/vent holes to be located in diametrically opposed positions and did not discuss the added complication of distribution around an embedded layer.
The present invention avoids the problem of gas entrapment without resorting to openings on opposite sides of the gasket. This enables better manufacturing flexibility, with less complicated handling and mold assembly design. Thus, although there have been attempts to solve the gas entrapment problem, none of the attempts discuss or address the added complication of distribution around an embedded layer with thermosetting resins.
Multiple or branched channels have been reported for delivery of different thermoplastic materials to injection molding systems [Ehritt, U.S. Pat. No. 4,789,318]. However, thermoset resins used in the present invention must be processed in an entirely different way than the thermoplastic materials of Ehritt, due to their opposite responses to increased temperature, e.g., thermosets harden while thermoplastics flow. Indeed, in thermoplastic processing, no flexible gasket is used and most operations occur at an increased temperature and pressure. Therefore, the Ehritt patent is not a suitable process for the thermoset processing of the present invention.
The apparatus and method of lens manufacture of the present invention allows equal or controlled differential, even sequential, distribution of thermosetting resin material, particularly around an embedded layer. While tabs or cut-outs in the embedded layer may be used to enhance this distribution, the present invention also allows controlled and distinctly improved delivery of thermosetting resin material when the embedded layer is impermeable. Since the present invention allows for reproducible and controlled delivery of a thermosetting material to both sides of an embedded layer, a lens can be manufactured with different optical or material properties on either side of the embedded layer.
Another benefit of the present invention is that more thermosetting material may be preferentially delivered to the back surface of the semi-finished lens while assuring the front surface is filled. Yet another benefit of the present invention is the control of distribution of the thermosetting resin material by the alteration of angle and the placement of port holes.
The importance of a controllable method and apparatus for side-fill manufacturing of lenses makes this method and apparatus amenable to a wide variety of applications such as reproducible positioning of embedded film in finished plano lenses, reproducible positioning of embedded film in semi-finished lenses, and reproducible introduction of a different compositions of materials to different sides of the embedded layer. For example, the invention enables the introduction of a composition comprising regular thermoset materials or higher impact-resistant materials to the back layer of the lens and introduction of a composition comprising the following materials, or a mixture of the following materials in front of the embedded layer: regular thermoset resin; higher impact-resistant material; abrasion-resistant material; photochromic material; tinted resin; high viscosity material; lower refractive index material; or higher refractive index material. The present invention may also be used to introduce thermoset materials containing inorganic or organic particles for increased hardness, or containing inorganic or organic colorants.
The present invention is also amenable to automatic or manual filling techniques. In automated filling processes, the port holes can be fitted with fill sensors to signal when the lens chamber is full and when the thermoset monomer flow can cease. Port holes can also be fitted with temperature or viscosity sensors to monitor and control the curing process. Similarly, port holes can be used to pull vacuum on the mold assembly for the removal of entrapped gases.
The invention described herein has overcome many of the deficiencies of the prior art noted above. The present invention provides a method of casting thermoset lenses that allows for the filling of the a mold assembly and for the egress of trapped gases within the mold assembly.
In particular, the method for making a thermoplastic lens comprises providing a composition comprising a thermosetting resin. A gasket means is obtained which supports mold members of a lens casting mold. The gasket means comprises an annular body formed by a cylindrical wall which has an inside surface and an outside surface; a plurality of port holes on the outside surface of the wall, each of the holes has a face surface on the outside surface and a passageway which extends therethrough. Each of the passageways has one end in the face surface of the port through which the passageway extends, and another end extends through the wall and opens at the lens chamber. The composition is placed in the passageway and the mold is filled. The side port holes are used for filling or venting of the lens chamber and can also be used for sensor positions.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following detailed description, appended claims, and accompanying drawings.